Portable flashlights use bulbs, such as incandescent lamps and light emitting diodes (LEDs), which are designed to operate at a rated voltage. The light output from the bulb is generally undesirably low when the bulb is operated at less than its rated voltage, and the bulb life is generally shortened when it is operated at greater than its rated voltage. The rated voltage therefore determines an output voltage of the power supply, which is generally provided by batteries that a particular flashlight will need to accommodate. For example, if a flashlight is being designed for a bulb having a rated voltage of 4.5V, then the flashlight will generally need to accommodate three 1.5V cells, such as standard “AAA”, “AA”, “C” or “D” cells.
The relationship between the rated voltage and the batteries causes manufacturers and distributors of flashlights to stock an undesirably large assortment of batteries to accommodate the various rated bulb voltages.